In a wide variety of applications it is advantageous or necessary to sense the position of a linearly or rotationally movable element. For example, in automobile seat applications the seat may be linearly movable, either manually or automatically via electro-mechanical means, on an associated track assembly. A sensor may provide a signal representative of the linear position of the seat on the track for a variety of purposes, e.g. to control deployment of an air bag, to control the electromechanical actuator that causes translation of the seat in connection with a seat position memory feature, etc.
For a seat position application, it is increasingly desirable for a sensor to provide multiple position outputs for purposes of ascertaining occupant position. For example, in applications where seat position is used to control air bag deployment early configurations involved only single stage air bag systems. A single stage air bag deploys with a known deployment force that may not be varied. In this application, seat position information was used only to determine when the airbag should be deployed. However, the advent of dual stage air bags, i.e. air bags that may be deployed with two distinct deployment forces, required increased resolution in position sensing. Also, the industry is now moving to variable stage airbags where the deployment force may be varied depending upon occupant position and classification. Variable stage airbag configurations require a sensor configuration that can detect multiple seat positions for use in determining the appropriate deployment force.
Another desirable feature of a position sensor, especially in the context of an automobile seat application, is that it be a non-contact sensor. A non-contact sensor includes a sensing element that does not physically contact the sensed object, allowing quiet operation of the sensor and minimizing wear. Preferably, the sensor operates with a relatively large air gap between the sensor and the sensed object to avoid inadvertent contact due to manufacturing or assembly variances.
Another issue associated with seat position sensors is that the seat track environment is very crowded with limited physical space for such sensors. Also the space available for the sensor may vary among vehicle types. As such, sensors which are compact in size are desirable.
Accordingly, there is a need for a seat position sensor that is compact in size and is configured to operate with a relatively large air gap.